1) Field of the Invention
The present invention relates to a negative feedback power supply apparatus for a load. For example, the present invention is applied to an apparatus for testing the AC magnetization characteristics of a toroidal core or a cut-core type core, a power supply apparatus for a load of a rectifier circuit, or a power supply apparatus for a load for a distorted current.
2) Description of the Related Art
In order to carry out a testing of the AC magnetization characteristics of a large number of toroidal cores, such as exciting currents, and a core loss such as a vortex current loss and a hysteresis loss, it is necessary to wind windings on a core for every test. To easily wind the windings on a core, connector-type contacts may be used to reduce the desorption of the windings. However, in the actual design of transformers or the like, since the thickness of the windings is as large as possible, to reduce the resistance value thereof, and the number of turns of the windings is large, a current flowing therethrough is small and the reduction in potential and heat generation by the resistance component of the windings is also small. Contrary to this, when the connector-type contacts are used, since the space for installing the connector-shaped contacts is restricted, the thickness of the windings is small and the number of turns of the windings is small. As a result, it is necessary to increase a test exciting current supplied to the primary winding, but such a current is affected by the resistances of the windings and the contacts.
In a prior art testing apparatus for a toroidal core having primary and secondary windings, an input AC power supply and an AC current meter are connected to the primary winding, and an AC voltage meter is connected to the secondary winding. Further, a power meter is connected between the primary winding and the secondary winding. In this apparatus, a measurement of a primary current I.sub.P and a measurement of a core loss are carried out at the periphery of a saturated magnetic flux, which is one of the AC magnetization characteristics to be tested. Note that the measurement of core loss is made by the power meter.
However, fluctuation of the equivalent DC resistance of the primary winding is caused by the heat generated by the exciting current, and fluctuation of the contact DC resistance of a connector-type contact is caused by the state of the contact. Further, fluctuation of the equivalent AC resistance of the primary winding is caused by the saturation characteristics of the core. Therefore, a large fluctuation occurs in the output voltage of the secondary winding. Further, at the periphery of a saturated magnetic flux density, an extraordinary current generated locally at one cycle of the AC current invites a spontaneous reduction in the equivalent AC resistance, and as a result, the waveform of the output voltage generated at the secondary winding is greatly distorted. This large fluctuation and distortion lead to the generation of a large fluctuation and distortion in the magnetic flux density of the core, which is very disadvantageous from the viewpoint of obtaining a definite AC magnetic flux density. Accordingly, to make the output voltage of the secondary winding constant, even when the voltage of the AC power supply is adjusted so as to correct the output voltage generated in the secondary winding W.sub.2, the distortion of the magnetic flux density waveform, i.e., the distortion of the output voltage, remains and, simultaneously, the peak current portion of the exciting current is suppressed. Therefore, it is impossible to carry out a correct measurement.